Mainly two search and recognition principles have been known heretofore:
(a) Passive
For searching and recognizing a flying body, radiation detectors have been used which operated in the visible and in the infrared spectral ranges for recognizing a target. An example of such a passive target search arrangement is given in the German Patent Publication 3,014,906. The operating principle described therein is, however, limited to a series or row arrangement of detectors and to the sampling or scanning thereof one after another in sequence. The number of usable single detectors is limited in such an arrangement, and the manner of target searching as well as the evaluation is made more difficult by time comparison and delay elements. PA1 Active systems are, for example, radar systems, or in general such systems in which electromagnetic radiation is transmitted out and the reflected radiation of a flying object illuminated in this manner, is received by appropriate sensors and analyzed. The sensors are also called electro-optical sensors, see for example, Microwave Journal, September, 1983, Nr. 9, page 121 et seq. The disadvantage of such a system is that its prominent characteristic emission can be detected by the enemy.
(b) Active